Added Close Pane to Context Menu (#15198)

## Summary of the Pull Request
Adding a 'Close Pane' menu item in the context menu.

## References and Relevant Issues
#13580 

## Detailed Description of the Pull Request / Additional comments
If a user decides to split a tab to create multiple panes through the
context menu, they should be able to then close the pane via the context
menu too. This PR introduces a new context menu item, 'Close Pane', that
only appears when a user has 2 or more panes in a tab. When a user
clicks close pane, the _active_pane will be closed.

## Validation Steps Performed

![close_pane_terminal](https://user-images.githubusercontent.com/98557455/232649000-8b521070-4f1b-4da9-8092-6ff802e91e2c.gif)

As it's my first PR, I still need to understand how to go through the
testing suite.

## PR Checklist
- [x] Closes #13580 
- [ ] Tests added/passed
- [ ] Documentation updated
- If checked, please file a pull request on [our docs
repo](https://github.com/MicrosoftDocs/terminal) and link it here: #xxx
- [ ] Schema updated (if necessary)

---------

Co-authored-by: Carlos Zamora <carlos.zamora@microsoft.com>

src/cascadia/TerminalApp/Resources/en-US/Resources.resw

@@ -763,15 +763,12 @@
   </data>
   <data name="AboutDialog_CheckingForUpdatesLabel.Text" xml:space="preserve">
     <value>Checking for updates...</value>
-    <comment></comment>
   </data>
   <data name="AboutDialog_UpdateAvailableLabel.Text" xml:space="preserve">
     <value>An update is available.</value>
-    <comment></comment>
   </data>
   <data name="AboutDialog_InstallUpdateButton.Content" xml:space="preserve">
     <value>Install now</value>
-    <comment></comment>
   </data>
   <data name="DuplicateRemainingProfilesEntry" xml:space="preserve">
     <value>The "newTabMenu" field contains more than one entry of type "remainingProfiles". Only the first one will be considered.</value>
@@ -820,4 +817,10 @@
   <data name="NewTabMenuFolderEmpty" xml:space="preserve">
     <value>Empty...</value>
   </data>
-</root>
+  <data name="ClosePaneText" xml:space="preserve">
+    <value>Close Pane</value>
+  </data>
+  <data name="ClosePaneToolTip" xml:space="preserve">
+    <value>Close the active pane if multiple panes are present</value>
+  </data>
+</root>

src/cascadia/TerminalApp/TerminalTab.cpp

@@ -33,6 +33,8 @@ namespace winrt::TerminalApp::implementation
         _rootPane = rootPane;
         _activePane = nullptr;
 
+        _closePaneMenuItem.Visibility(WUX::Visibility::Collapsed);
+
         auto firstId = _nextPaneId;
 
         _rootPane->WalkTree([&](std::shared_ptr<Pane> pane) {
@@ -517,6 +519,9 @@ namespace winrt::TerminalApp::implementation
         // original pane first.
         auto [original, newPane] = _activePane->Split(splitType, splitSize, pane);
 
+        // After split, Close Pane Menu Item should be visible
+        _closePaneMenuItem.Visibility(WUX::Visibility::Visible);
+
         // The active pane has an id if it is a leaf
         if (activePaneId)
         {
@@ -1071,6 +1076,11 @@ namespace winrt::TerminalApp::implementation
             _mruPanes.insert(_mruPanes.begin(), paneId.value());
         }
 
+        if (_rootPane->GetLeafPaneCount() == 1)
+        {
+            _closePaneMenuItem.Visibility(WUX::Visibility::Collapsed);
+        }
+
         _RecalculateAndApplyReadOnly();
 
         // Raise our own ActivePaneChanged event.
@@ -1326,6 +1336,23 @@ namespace winrt::TerminalApp::implementation
             Automation::AutomationProperties::SetHelpText(splitTabMenuItem, splitTabToolTip);
         }
 
+        Controls::MenuFlyoutItem closePaneMenuItem = _closePaneMenuItem;
+        {
+            // "Close Pane"
+            closePaneMenuItem.Click([weakThis](auto&&, auto&&) {
+                if (auto tab{ weakThis.get() })
+                {
+                    tab->ClosePane();
+                }
+            });
+            closePaneMenuItem.Text(RS_(L"ClosePaneText"));
+
+            const auto closePaneToolTip = RS_(L"ClosePaneToolTip");
+
+            WUX::Controls::ToolTipService::SetToolTip(closePaneMenuItem, box_value(closePaneToolTip));
+            Automation::AutomationProperties::SetHelpText(closePaneMenuItem, closePaneToolTip);
+        }
+
         Controls::MenuFlyoutItem exportTabMenuItem;
         {
             // "Export Tab"
@@ -1377,6 +1404,7 @@ namespace winrt::TerminalApp::implementation
         contextMenuFlyout.Items().Append(renameTabMenuItem);
         contextMenuFlyout.Items().Append(duplicateTabMenuItem);
         contextMenuFlyout.Items().Append(splitTabMenuItem);
+        contextMenuFlyout.Items().Append(closePaneMenuItem);
         contextMenuFlyout.Items().Append(exportTabMenuItem);
         contextMenuFlyout.Items().Append(findMenuItem);
         contextMenuFlyout.Items().Append(menuSeparator);

src/cascadia/TerminalApp/TerminalTab.h

@@ -113,6 +113,8 @@ namespace winrt::TerminalApp::implementation
         std::shared_ptr<Pane> _activePane{ nullptr };
         std::shared_ptr<Pane> _zoomedPane{ nullptr };
 
+        Windows::UI::Xaml::Controls::MenuFlyoutItem _closePaneMenuItem;
+
         winrt::hstring _lastIconPath{};
         std::optional<winrt::Windows::UI::Color> _runtimeTabColor{};
         winrt::TerminalApp::TabHeaderControl _headerControl{};